The objective of this study was to observe the differences in alternative splicing between human and nonhuman primate brains, paying close attention to the lineage-specific changes in splicing during the evolution of humans diverging from chimpanzees.
During the study tissue samples of humans, chimpanzees and rhesus macaques were taken and a microarray analysis of alternative splicing, including RT-PCR tests of brain transcriptomes was performed.
Alternative splicing is a form of gene regulation in eukaryotes where information from DNA is transcribed into a messenger RNA (mRNA) template from a precursor transcript. The process involves selective removal or retention of exons and introns from the developing RNA.
The analysis of splicing patterns in the primate brain were studied by high-density exon junction array profiling of brain transcriptomes of the three species. When comparing human and nonhuman primates transcriptomes changes in transcript levels during human evolution had been observed. These changes can account for the phenotypical and genomic differences of which distinguishes each species from one another.
During the examination of the brain transcriptomes, splicing differences were discovered in 509 genes between the three species. RT-PCR analysis indicated that from 40 exons, there was a confirmed splicing evolution of 33 exons. With the support of the analysis of rhesus macaques, it was confirmed that 13 of the 33 human-specific exons had an increase or decrease in transcript levels and revealed widespread changes of the alternative splicing of brain transcriptomes during human and primate evolution.
These results included a significant increase in the rate of silent substitutions within exon, coupled and accelerated sequence divergence in flanking introns. Indicating that evolution of cis-regulatory signals had helped contribute to human-specific splicing patterns (Lin, L. et al. 2010).
In a similar study (Reyes, A. et al. 2013) there is conflicting evidence regarding exon usage and how it can vary between species due to genetic variations in cis-regulatory regions. They found that when comparing transcriptomes of several human subjects there had been several erroneous splicing in low abundance isoforms. This gave a prominent difference in splicing between close species like humans and chimpanzees. Also, they found after analyzing transcriptomes of physiologically similar organs of mammalian and vertebrate species, splicing variation between these species exceeds the within-species variation across tissues which contradicts the previous studies analysis that gene expression levels in which patterns show strong conversation.
In another study (Barbosa-Morais, N. et al. 2012) it was said that rapid divergence in alternative splicing patterns in vertebrate organs played more of a role in species-specific differences than did changes in mRNA expression (gene expression). Which agreed with the findings that mRNA expression had shown evidence of distinguishing genes between the different species. It was said that re-assortment of splicing code can explain the differences between vertebrate species. Due to these alternative splicing changes affecting trans-acting factors involved in gene regulation, there can be an explanation for the difference in diversification in alternative splicing and changes within phenotypic change between the three previously mentioned species.